In recent years, there have been ever-increasing demands for high-density optical disks, and in order to meet these demands a variety of recording systems have been proposed. As one of the recording systems for achieving such high-density optical disks, a land/groove recording system has been studied. The land/groove recording system is a system in which recording is made on both the lands and grooves formed on an optical disk, and in this case, it is necessary to preliminarily record address information on both the lands and grooves. For example, Japanese Laid-Open Patent Publication No. 314538/1993 (Tokukaihei 5-314538) and Japanese Laid-Open Patent Publication No. 301976/1994 (Tokukaihei 6-301976) disclose recording methods for address information in the land/groove recording system.
Referring to FIG. 14, the following description will discuss the detection system of address signals disclosed in the above-mentioned Japanese Laid-Open Patent Publication No. 314538/1993 (Tokukaihei 5-314538). On an optical disk, grooves 1 and lands 2 are formed in a spiral shape or in the shape of concentric circles, and the grooves 1 and lands 2 are designed so that the average values of the widths thereof are equal to each other, and also equal to the track pitch. Here, address information is recorded by making one of the side walls 1W of each groove 1 wind in accordance with addresses. Upon reproduction, a light spot 4, which has a diameter smaller than twofold the groove width or the land width, is used for detecting winding frequencies of the winding side wall 1W from tracking error signals so that the address information is obtained.
However, the above-mentioned detection system for address signals poses problems in which since the widths of the grooves 1 and the lands 2 vary depending on places, the reflectivity varies, thereby causing degradation in information reproducing signals; furthermore, the detection system for address signals also poses problems in which tracking offsets tend to occur in the light spot 4, thereby giving adverse effects on the reproducing signal.
Moreover, in the recording method for address information described in the above-mentioned Japanese Laid-Open Patent Publication No. 301976/1994 (Tokukaihei 6301976), the groove width and the land width are changed in accordance with address signals in an address recording area. Upon reproduction, address information is obtained by utilizing circumstances in which the total quantity of reflected light from the optical disk changes in response to the groove width or the land width.
However, since the total quantity of reflected light from the optical disk tends to be affected by variations in the quantity of laser light, variations in the groove width, a difference in reflectivity in each disk, etc., a complex system is required for preventing such adverse effects.
Furthermore, another problem with the two conventional systems is that since the widths of the lands and grooves are not constant, there is difficulty in manufacturing the disks.